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Resveratrol Radical Repair by Vitamin C at the Micelle–Water Interface: Unexpected Reaction Rates Explained by Ion–Dipole Interactions
Author(s) -
Kerzig Christoph,
Hoffmann Matthias,
Goez Martin
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201705635
Subject(s) - micelle , ascorbic acid , chemistry , photochemistry , aqueous solution , radical , cationic polymerization , organic chemistry , food science
Repair reactions of lipophilic phenoxy radicals by hydrophilic co‐antioxidants at model membranes are important for understanding the factors that govern the interactions between radical scavengers in biological systems. By using near‐UV photoionization, we have selectively generated the phenoxy radical of the famous antioxidant resveratrol inside anionic (SDS), cationic (DTAC), or neutral (TX‐100) micelles, as well as in homogeneous aqueous solution, and have compared its repairs in these media by the water‐soluble co‐antioxidants ascorbic acid and ascorbate monoanion. With all surfactants, these reactions are dynamic processes at the micelle–water interface. Whereas for the combinations ascorbate monoanion/ ionic micelle the repair rates can be rationalized by the Coulombic interactions, unexpected effects were observed with the neutral ascorbic acid and the charged micelles: for the anionic micelles, this repair is three times faster than in homogeneous solution, and two orders of magnitude faster than for the cationic micelles. Given that the repair by a concerted proton–electron transfer demands a coplanar arrangement of the resveratrol phenoxy centre sticking out into the Stern layer and the co‐antioxidant hydroxy moiety approaching from the aqueous bulk, we explain these results by ion–dipole interactions: only at a negatively charged micellar surface does the direction of the large dipole moment of ascorbic acid lead to an orientation favourable for the repair.